Many hydrocarbon-producing fields contain hydrocarbons of sufficiently high viscosity that the hydrocarbons do not flow freely toward a production well. The movement of these hydrocarbons toward a production well is assisted by the injection of steam to heat the formation and reduce the viscosity of the hydrocarbons, thus permitting them to flow toward the production well. Many of these fields contain different hydrocarbon-producing formations or zones which are separated by non-producing formations. It is often desirable to simultaneously produce hydrocarbons from these different zones. In order to maximize the efficiency of the operation and minimize costs, it is desirable to inject steam only into those portions of the formation that contain hydrocarbons.
If the wellbore casing is sufficiently large, individual injection tubing strings can be run into the wellbore to the desired formation so that the compressible injected fluid, such as steam, nitrogen, carbon dioxide and the like, is directed toward the specific producing zone of interest. However, many wellbores have a sufficiently small diameter that only a single tubing string can be inserted into the casing. When such wells penetrate formations having different producing zones, it may be prohibitively expensive to redrill the well in order to put separate injection tubing strings within the casing. Thus, it is highly desirable to have a method of simultaneously injecting steam of a known quality and quantity into different and separate producing zones so as to maximize the production from these individual formations.
U.S. application Ser. No. 716,292, now U.S. Pat. No. 4,640,355, titled "Limited Entry Method For Multiple Zone Compressible Fluid Injection", filed Mar. 26, 1985, discloses an apparatus and method for using downhole critical flow chokes that permit the accurate determination of the quality and quantity of steam injected into a particular producing zone. Although the application describes the overall concept for implementing the injection of known quantities and qualities of steam in separate formations, it would be highly desirable to have a particular apparatus for use in a single tubing string that would permit the injection of steam into different producing zones while permitting the running of logging tools or other instruments into and out of the injection tubing string to determine parameters of the surrounding formation so that the injection of the compressible fluid, its composition quality and quantity can be optimized to minimize costs and maximize production from a particular producing zone.